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  • 1
    Publication Date: 2015-09-21
    Description: As part of the PeECE II mesocosm project, we investigated the effects of pCO2 levels on the initial step of heterotrophic carbon cycling in the surface ocean. The activities of microbial extracellular enzymes hydrolyzing 4 polysaccharides were measured during the development of a natural phytoplankton bloom under pCO2 conditions representing glacial (190 µatm) and future (750 µatm) atmospheric pCO2. We observed that (1) chondroitin hydrolysis was variable throughout the pre-, early- and late-bloom phases, (2) fucoidanase activity was measurable only in the glacial mesocosm as the bloom developed, (3) laminarinase activity was low and constant, and (4) xylanase activity declined as the bloom progressed. Concurrent measurements of microbial community composition, using denaturing-gradient gel electrophoresis (DGGE), showed that the 2 mesocosms diverged temporally, and from one another, especially in the late-bloom phase. Enzyme activities correlated with bloom phase and pCO2, suggesting functional as well as compositional changes in microbial communities in the different pCO2 environments. These changes, however, may be a response to temporal changes in the development of phytoplankton communities that differed with the pCO2 environment. We hypothesize that the phytoplankton communities produced dissolved organic carbon (DOC) differing in composition, a hypothesis supported by changing amino acid composition of the DOC, and that enzyme activities responded to changes in substrates. Enzyme activities observed under different pCO2 conditions likely reflect both genetic and population-level responses to changes occurring among multiple components of the microbial loop.
    Type: Article , PeerReviewed
    Format: text
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  • 2
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    Inter Research
    In:  Marine Ecology Progress Series, 219 . pp. 1-10.
    Publication Date: 2018-05-28
    Description: The carbon and nitrogen content of transparent exopolymer particles (TEP) was determined and related to the concentration of TEP as quantified by a colorimetrical method. TEP were produced in the laboratory from dissolved precursors by laminar or turbulent shear. Dissolved precursors were obtained by 0.2 µm filtration from diatom cultures, with or without nutrient reduction, and from natural diatom populations. The relationship between carbon and TEP was significant, linear and species-specific. Carbon concentration of TEP derived from this relationship concurred with previous findings. Shortage of silicic acid or nitrate in the culture media had no effect on the carbon content of TEP. Molar C:N ratios of TEP were above the Redfield ratio, with a mean value of 26. It is suggested that the nitrogen fraction of TEP can be explained by adsorption of dissolved organic nitrogen (DON) onto TEP. Based on the newly established relationship, concentrations of TEP-derived carbon (TEP-C) were calculated for the Baltic Sea, the coastal Pacific, the North East Atlantic and the Northern Adriatic Sea.
    Type: Article , PeerReviewed
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  • 3
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    Elsevier
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 42 (1). pp. 99-109.
    Publication Date: 2016-08-02
    Description: The role of TEP (Transparent Exopolymer Particles) in the flocculation of a diatom bloom was studied under controlled conditions in a mesocosm. The concentration of TEP increased exponentially during growth, flocculation and senescence of the bloom. Aggregation began dominating the particle dynamics of TEP during the early growth phase of the bloom, several days prior to the appearance of large flocs and nutrient depletion. TEP aggregated with themselves and with phytoplankton due to the high stickiness of TEP, but phytoplankton was not observed to aggregrate with itself. The production of TEP, estimated from changes in concentration, did not increase after nutrients were depleted. The concentration of TEP was a linear function of chl a and particulate organic carbon (POC), indicating that production of TEP was linked to growth rather than standing stocks of phytoplankton. The ratio between TEP and phytoplankton appeared to be one of the factors determining the onset of the flocculation of the bloom. The concentration of TEP may have been decreased by bacterial degradation. Bacterial degradation of TEP may explain the low TEP to chl a values, the decrease in stickiness of particles as the bloom progressed, and the retarded onset of flocculation.
    Type: Article , PeerReviewed
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  • 4
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    Elsevier
    In:  FEMS Microbiology Ecology, 46 (3). pp. 247-255.
    Publication Date: 2020-03-20
    Description: Observations that the majority of silica dissolution occurs within the upper 200 m of the ocean, and that sedimentation rates of diatom frustules generally do not decrease significantly with depth, suggested reduced dissolution rates of diatoms embedded within sinking aggregates. To investigate this hypothesis, silica dissolution rates of aggregated diatom cells were compared to those of dispersed cells during conditions mimicking sedimentation below the euphotic zone. Changes in the concentrations of biogenic silica, silicic acid, cell numbers, chlorophyll a and transparent exopolymer particles (TEP) were monitored within aggregates and in the surrounding seawater (SSW) during two 42-day experiments. Whereas the concentration of dispersed diatoms decreased over the course of the experiment, the amount of aggregated cells remained roughly constant after an initial increase. Initially only 6% of cells were aggregated and at the end of the experiment more than 60% of cells were enclosed within aggregates. These data imply lower dissolution rates for aggregated cells. However, fluxes of silica between the different pools could not be constrained reliably enough to unequivocally prove reduced dissolution for aggregated cells.
    Type: Article , PeerReviewed
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  • 5
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    NATL ACAD SCIENCES
    In:  EPIC3Proceedings of the National Academy of Sciences of the United States of America, NATL ACAD SCIENCES, ISSN: 0027-8424
    Publication Date: 2016-07-04
    Description: The 2010 Deepwater Horizon oil spill resulted in 1.6–2.6 × 1010 grams of petrocarbon accumulation on the seafloor. Data from a deep sediment trap, deployed 7.4 km SW of the well between August 2010 and October 2011, disclose that the sinking of spill-associated substances, mediated by marine particles, especially phytoplankton, continued at least 5 mo following the capping of the well. In August/September 2010, an exceptionally large diatom bloom sedimentation event coincided with elevated sinking rates of oil-derived hydrocarbons, black carbon, and two key components of drilling mud, barium and olefins. Barium remained in the water column for months and even entered pelagic food webs. Both saturated and polycyclic aromatic hydrocarbon source indicators corroborate a predominant contribution of crude oil to the sinking hydrocarbons. Cosedimentation with diatoms accumulated contaminants that were dispersed in the water column and transported them downward, where they were concentrated into the upper centimeters of the seafloor, potentially leading to sustained impact on benthic ecosystems.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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